﻿//
// SynchronizationContextTaskScheduler.cs
//
// Author:
//       Marius Ungureanu <maungu@microsoft.com>
//
// Copyright (c) 2018 Microsoft Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace MonoDevelop.Core
{
	// Based on CoreCLR's implementation of the TaskScheduler they return from TaskScheduler.FromCurrentSynchronizationContext
	class SynchronizationContextTaskScheduler : TaskScheduler
	{
		readonly SendOrPostCallback _postCallback;
		readonly SynchronizationContext _synchronizationContext;

		internal SynchronizationContextTaskScheduler (SynchronizationContext synchronizationContext)
		{
			_postCallback = new SendOrPostCallback (PostCallback);
			_synchronizationContext = synchronizationContext ?? throw new ArgumentNullException (nameof (synchronizationContext));
		}

		public override int MaximumConcurrencyLevel => 1;

		protected override void QueueTask (Task task) => _synchronizationContext.Post (_postCallback, task);

		protected override bool TryExecuteTaskInline (Task task, bool taskWasPreviouslyQueued) =>
			SynchronizationContext.Current == _synchronizationContext && TryExecuteTask (task);

		protected override IEnumerable<Task> GetScheduledTasks () => null;

		void PostCallback (object obj) => TryExecuteTask ((Task)obj);
	}
}
